1. Technical Field
The present invention relates to a magnetic layer composition including NiZn ferrite, a multilayer type coil component including a magnetic layer prepared therefrom, and a method for manufacturing the same.
2. Description of the Related Art
A multilayer type chip inductor, a multilayer type chip bead, and a module type product in which an embedded coil is contained, employ a NiCuZn ferrite material as a body material. In addition, since a conductor resistance has a large effect on inductance characteristics of the product (quality factor Q, thermal characteristics), 100% silver (Ag) is used for an internal electrode. Therefore, in order to allow the NiCuZn ferrite material to be sintered at a temperature of 960□ or lower, which is a melting point of silver, powder characteristics thereof or other additives are being developed.
Meanwhile, silver for the internal electrode, which is a noble metal, is not oxidized at a high temperature, and thus, a de-binder process (removing organic substance from a half-finished product at a high temperature) and a sintering process may be performed under a general atmosphere.
Meanwhile, the silver used for the internal electrode has the lowest resistivity as compared with other metals, and thus has many advantages. However, silver is expensive because it is a noble metal, and temporal price variation thereof is very large. Recently, a great increase in the price of silver imposes a heavy burden on product costs. Several kinds of metals generally usable for the internal electrode, except this silver, are shown in Table 1. Except copper (Cu), most have very large resistivity as compared with silver, and thus, they are not suitable as a conductor for a general coil component except for special usages regardless of low efficiency. Furthermore, copper is also easily oxidized, and thus, is not still used.
TABLE 1ResistivityMeltingCoefficient Of(×1E−8 Ω · m,Densitypointthermal Expansion298K)(g/cc)(° C.)(×10E−6/K)NotesAg1.5910.596119.2Au2.3519.3106314.2Pt10.621.420459Pd10.812182511.2Cu1.78.96108316.5Ni6.848.9145313.3MagneticmaterialMo5.210.226105.43W5.6519.334104.59
A procedure for forming a coil in a general multilayer type coil element of the related art is shown in FIG. 1. Referring to the drawing, the multilayer type coil element is manufactured by forming a via hole 20 for interlayer interaction in a ceramic sheet 10 including organic substance, which is prepared through tape molding, and then printing (commonly, by using screen printing) a silver internal conductive paste (internal electrode 30) on the ceramic sheet through the via hole 20 to form a pattern. The patterns thus printed are laminated in alignment with accurate positions, and connection of the silver paste through the via hole is performed, thereby entirely forming a coil. The coil type half-finished product is cut into separate chips, and hot air is applied thereto under the atmosphere to remove organic substance (de-binder). The resulting product is fired in a furnace at a high temperature of 800□ or higher, thereby forming a chip inductor.
Meanwhile, when copper is used as an internal conductor, sintering under a reducing ambience with less oxygen needs to be performed in order to prevent the copper from being oxidized. However, at this time, the NiCuZn ferrite, which is a general material for the multilayer type coil element, has poor resistance to reduction, and thus, reduction of the material causes breakage of structure, deterioration in magnetic characteristics, and prevention of densification by sintering. These results can be confirmed from X-ray diffraction as shown in FIG. 2.
FIG. 2 shows an X-ray diffraction pattern of NiCuZn ferrite sintered under a reducing ambience, and it can be seen that respective materials constituting the ferrite all were reduced to exhibit no peaks, and only peaks of other constituent components except for the ferrite were observed.
Therefore, it is necessary to develop new materials that substitute for silver, which is a noble metal, as the internal conductor, and methods for utilizing the existing materials as the internal conductor.